Donald Trump boiled his decadent campaign down to one theme during the presidential debate on Sunday night: hatred of Hillary and Bill Clinton.

With knock-kneed Republican officeholders showing signs of summoning the nerve to desert him, Mr. Trump labored to demonize Hillary Clinton — blaming her even for his own failure to pay taxes — and to remind his core supporters that he is all that stands between her and the presidency.

If he were in charge, Mr. Trump told Secretary Clinton at one point, “You’d be in jail.”

When Mrs. Clinton called Mr. Trump out for his failure to apologize to the minorities, immigrants and women he’s offended, he responded by promising vengeance. Should he win, he said, he would unleash a special prosecutor to investigate her.

Sniffing and glowering, Mr. Trump prowled behind Mrs. Clinton as she presented herself again as the only adult on stage, the only one seeking to persuade the great majority of Americans that she shares their values and aspirations. Mr. Trump, by contrast, fell back on the tricks he has learned from his years in pro wrestling and reality television, making clear how deep his cynicism goes.

Just before the debate, desperate to shift attention from his pattern of harassment, Mr. Trump sat hunched over a blank notepad in a hotel meeting room, encouraging four women to face the cameras and tell their stories of sexual victimization. “You went through a lot,” Mr. Trump coaxed one of the women flanking him, as he bent their allegations against Bill and Hillary Clinton to serve himself. The women’s claims deserved to be investigated and aired, and they have been, repeatedly.

During the debate, Mr. Trump struggled once again to coherently explain his policies, instead wandering down twisting, shadowy alleyways in muttering pursuit of his various claims about Mrs. Clinton, including that she, not he, was responsible for his birther lie about President Obama. He complained that the moderators were ganging up on him and failing to question Mrs. Clinton about her private email server — immediately after they had done just that.

Mr. Trump probably performed well enough to silence the 11-hour whispering campaign among Republicans about somehow ejecting him from the ticket. That means the G.O.P. will continue asking Americans to vote for a candidate who is debasing and trivializing our politics. During the debate, it seemed somewhere between poignant and futile to hear the moderators invite undecided voters to ask about his plans for the nation.

When Mr. Trump so grandly accepted the Republican nomination in July, he said, “I have joined the political arena so that the powerful can no longer beat up on people that cannot defend themselves.” By then, though, he had already campaigned for months by beating up on vulnerable Americans, including minorities and the disabled. Only in recent days has the Republican establishment started to acknowledge the magnitude of his hypocrisy.

The videotape disclosed Friday provided gruesome evidence that the Republican standard-bearer has for years used his powerful status to prey on women. Other revelations followed, including that in 2005 he told Howard Stern on his radio show that, when he owned the Miss Universe pageant, he made a practice of “inspecting” naked contestants backstage. “You know, they’re standing there with no clothes. … And you see these incredible-looking women, and so, I sort of get away with things like that.”

Now, as he struggles to close the biggest deal of his lifetime, a woman is getting the better of him. That’s not surprising, but it is apt.